So as to prevent the surface of steel sheet from corrosion and expand its life, a zinc layer is usually coated to the surface of steel sheet. The steel sheet coated with zinc is called galvanized steel sheet.
Sometimes, a “post-plating surface treatment” needs to be consequently applied to the galvanized steel sheet that is just produced. The post-plating surface treatment prepares the surface for the subsequent forming or coating processes, and also provides a short-term protection of the galvanized steel sheet during subsequent handling process, storage and transportation. Currently, many surface treatment technologies have been used in industry, such as phosphorization, chromate treatment, oil coating, and their variants and combinations.
Chromate treatment began to be used in industry since 1930s, and it once became the most widely-used technology of the steel sheet surface treatment. Chromate treatment can provide a short-term protection from rust and corrosion. The process of chromate treatment is that, a solution of chromic acid, chromium salts and inorganic acid generate a thin conversion layer on the metal surface, the chemical reaction between metal and solution dissolution of metal, and leads to form a protective film of complex chromium and metal compounds. This method is of simple process, low cost and good corrosion resistance. However, the chromium compounds in the coating film, especially compounds of hexavalent chromium, are seriously harmful to human body and environment.
In order to seek an environmentally friendly technology, in recent years a variety of non-chromium organic or inorganic surface treatment technologies have been developed, such as inorganic conversion film system containing molybdenum, vanadium or zirconium, aqueous polymer dispersions-silica system and aqueous polymer dispersions-silicate system, etc.
At present, the introduction of silicon-containing organic-inorganic hybrid materials into the surface treatment of galvanized sheet is one of the hot issues in research. The silane has been used as anti-corrosion agent for metal surface for a long time, such as: in U.S. patent No. 20030049486A1, US20050058843A1 and EP 1153089B1, a composition of a vinyl silane and alkyl-silane was introduced to treat metal (mainly zinc) surface, while U.S. Pat. No. 6,955,728B1 treat the zinc surface by an treatment agent containing acyloxy silane.
CN1887449A and CN1887451A use a composition of silane, water-soluble polymers and vanadium compound as a surface treatment agent for galvanized steel sheet so as to realize the surface of the steel plate alkali resistant and solvent resistant. However, the anti-corrosion effect of these surface treatment agents is not satisfactory, or these agents contain toxic heavy metals; therefore, it's urgent to seek a new surface treatment agent for galvanized steel sheet which maintains the excellent corrosion resistance and are more environmentally friendly.